Snowy wonderlands, tropical beaches, skiing trips, what’s not to love when winter swings around? For aviation sector apart from the perils the season offers, aircraft and airfields can become heavily compromised in weather. Weather conditions play a significant role in the number of aviation incidents worldwide. With winter on the way, it is time to be equipped and ready for safer aviation operations on what could be sometimes, quite challenging days. It is especially important to be safe during winter when several factors can result in contamination of critical surfaces and components and affect an aircraft’s dynamics. Aircraft De-icing is an essential part in ground operations especially during winters to ensure the safety of passengers and crew during winter.
The procedure of de-icing and anti-icing aircrafts are carried out using various techniques. The most common technique involves the use of FPD (freezing point depressant) fluids to aid in the ground de-icing/anti-icing process and to prevent frost, snow, or ice from forming on the aircraft. It is mandatory to incorporate the Aviation solutions providers should incorporate the Anti Icing Code Procedure into their operational procedures
The purpose of aircraft de-icing and anti-icing procedures is threefold:
• To remove any frozen or semi frozen moisture from critical external surfaces of an aircraft before flight
• To protect those surfaces from the effects of such contaminants between treatment and airborne transmission
• To prevent subsequent contamination of external surfaces, any frozen or semi-frozen moisture should be removed from engine intakes and fan blades before takeoff
The Factors That Affect De/Anti-Icing
An aero plane’s surface roughness can be caused by a multitude of variables, some of them being:-
• Temperature of the environment
• Airplane crust temperature
• Water content and precipitation rate
• Temperature of deicing/anti icing fluids
• Fluid/water ratio of the de-icing/anti-icing fluid
• The speed and direction of the wind
Icing Types in Aviation
The three major types of ice accretion are as follows
Clear ice: forms when large drops hit the aircraft and freeze slowly.
Rime ice: forms when small drops hit the aircraft and freeze rapidly and looks like super thick frost.
Mixed ice: mixture of clear and rime ice.
Frost: Ice crystal deposits formed by sublimation when the departure and dew point are below freezing.
De-Icing/Anti-Icing Fluids for Airplanes
There are four types of deicing/anti-icing fluids: Type I, Type II, Type III, and Type IV.
Type I has a relatively low viscosity, which varies primarily with temperature. A fluid with type II, III or IV contains a thickener system and has a higher viscosity ,fluid/water ratio, and temperature changes. The anti-icing properties of Type II, III, and IV fluids are better than those of Type I fluids. Operators, fluid manufacturers, and airplane manufacturers must all establish use criteria for de-icing/anti-icing fluids, and they must also meet ISO (International Standards Organization) specifications.
For de-icing (removing existing contamination) a fluid called propylene glycol is used. This orange-colored fluid is heated to around 60-65 degrees Celsius and sprayed over the aircraft under pressure, blasting off any existing snow, ice or slush.
Differences Between De-Icing and Anti-Icing Fluids?
It is essential for Type I to be effective as an aircraft deicing fluid. Type I fluids are often further diluted for application due to aerodynamic performance and/or freezing points. Type II and IV fluids are used undiluted for maximum anti-icing protection. They are also used in diluted conditions when temperatures are high and precipitation is low for de-icing/anti-icing applications. Type III are diluted fluids classified as Type II or IV if they meet aerodynamic performance requirements. Due to high viscosity, Type II, III, and IV fluids coat the wings much thicker than Type I fluids. Airflow during take-off exposes these fluids to a shear force that causes to lose viscosity, streaming off before rotation.
Aircraft de-icing can be done at any airport where winter operations are carried out. During winter it is standard procedure to de-ice certain aircraft before every flight or when required. Depending on the available infrastructure, aircraft can be de-iced either at their gate or stand, after pushback, or at designated de-icing pads. The latter is usually only done at larger airports, as smaller airports often do not have any fixed locations for de-icing practices. De-icing is done just before the aircraft is departing as built-up ice, snow etc. can affect aircraft aerodynamics. When reaching rotation speed which is around 100 knots for most private aircrafts, majority of anti-icing fluids will be blown off the aircraft, with remaining fluids disappearing when aircraft reaches 1,000 feet above the ground.
How long does de-icing last?
Holdover Time is defined as the time between the application of de-icing fluids and the aircraft’s take-off. Once the aircraft is de-iced, it should not require another round of de-icing within the holdover time. The exact holdover time depends on the specific type and brand of fluids and governing aviation authorities In general, the holdover time for de-icing fluid will usually be around 20 minutes. Anti-icing liquids have a longer holdover time, which can be anywhere from 10 minutes to over 2 hours, depending on weather conditions
Prior to flight planning procedures and when weather conditions are conducive following precautions need to be followed: –
-All airframe critical surfaces should be examined thoroughly to determine if any contamination exists
-De-Icing Fluids and/or Anti-Icing Fluids should be applied correctly, along with the De/Anti-Icing Code
-Holdover Time (HOT) should be identified and monitored by the flight crew
Including the latest Holdover Time (HOT) Tables should be included in every AOM or POH (Pilot’s Operating Handbook) for flight crews.
-Providers of ground deicing/anti-icing should follow effective Quality Control procedures to ensure proper procedures are followed. Aircraft operators should ensure that ground de/anti-icing procedures are included in their Quality Assurance procedures.
-De/Anti-Icing Codes should be always used for communicating and documenting
Check Procedures for De-Icing and Anti-Icing
-Ground crews or flight crews usually perform the pre-flight walk-around or pre-flight check as the first step. In accordance with an approved operator plan, critical surfaces, fuselage, and landing gear are checked for ice, snow, slush, or frost. De-Icing and Anti-Icing operation are performed on an airplane if it is discovered to be iced or frosty.
-After De-Icing and Anti-Icing Fluids are Applied Qualified personnel will carry out an examination following the application of de-icing/anti-icing fluids.
Pre-takeoff checks are performed by the pilot-in-command to ensure that the airplane’s critical surfaces are clear of snow or frost before takeoff.
Other Critical Conditions
In rainy or high-humidity conditions for certain types of aircraft a thorough examination on the icing conditions may be required. To detect type of icing, special procedures must be included in the approved operator program.
Aerocontrol provides ground handling, ground operations and flight planning globally. To know more about our De-Icing services, contact us today